After a chapter analyzing Heidegger's Dasein Analytik as it is delineated in Sein und Zeit, in using, in large measure, an author coming from the anglo-american tradition, the A begins a quasi-commentary analysis of the second chapter of Heidegger's Die Grundprobleme der Phänomenologie, heretofore GP or (The Basic Problems of Phenomenology). This quasi-commentary method of analysis is required due to the informal nature of presentation, insofar as this GP text is a transcription of Heidegger's 1927 summer course at Marburg.
The A's chapter 3 analyzes the essence and existence distinction as it is found (or it's equivalent in Scotus's case) in Aquinas, Scotus and Suarez. In terms of inspiration it soon becomes clear – even on a vocabulary level - that Heidegger's views are heavily influenced by Suarez and his doctrines, particularly from his Disputationes Metaphysicae, DM.
Whereas Heidegger pretends to analyze Aquinas, Scotus and Suarez, each in his own right, the reality is that Suarez is the 'guiding light' throughout these three central, chapter 2 subsection GP analyses, (Alpha = Aquinas, Beta = Scotus and Gamma = Suarez). An obvious sign of this is Heidegger's bringing Giles of Rome and his famous duae res version of the essence and existence distinction into the Aquinas analysis. Although he got the idea from Suarez, Heidegger is slightly more affirmative than Suarez himself in attributing this at first startling version to Aquinas. (In a word, holding to the real distinction means being an Aegidian and Aquinas is said to hold to the real distinction.)
The A makes extensive use of contemporary Aquinas analysis to show that the essence and existence distinction doctrine that emerges from Aquinas's Aristotle commentaries is far from resembling Giles's. Via analysis of Metaphysics, V, 7, two Quodlibetal questions and Book II of the Posterior Analytics commentary (Lectios 1-10), a simpler doctrine emerges as to what we are doing when we predicate existence and essence of material substances. Not only is this not a duae res doctrine but one that can be explained without talking about real distinctions at all! (Heidegger's views on Scotus and Suarez are at once penetrating and much more predictable.)
The A next presents a chapter on Heidegger and Luther, showing the centrality of the theme 'betrayal of the tradition' in both figures.
In a final chapter, the A examines Heidegger's 1929 analysis of what the subject matter of metaphysics is, from his Die Grundbegriffe der Metaphysik (The Fundamental Concepts of Metaphysics). Heidegger claims that, for the medieval, ontotheological tradition, the oldest and most sacred, i.e., God, is the subject matter of metaphysics. (This includes Heidegger's accusation that medieval ontology is faith buttressed.)
Using a contemporary phenomenologist's and a medievalist's analysis, the A tries to show that Aquinas's commentary on Aristotle's Metaphysics reveals the subject matter of metaphysics not to be 'God', but ens commune. This philosophical conclusion is of course consequential for Heidegger's accusation that medieval ontology is faith supported.
The A concludes that an examination of Aquinas's Aristotle commentaries would have led to other conclusions than Heidegger's on what the subject matter of metaphysics is as well as on Aquinas's views on predicating essence and existence.